Filament tensioning method and electrical device having improved filament tensioner



May 9, 1950 H. K. ISHLER 2,506,374

' FILAMENT TENSIONING METHOD AND ELECTRICAL DEVICE HAVING IMPROVED FILAMENT TENSIONER Filed June 8, 1946 2 Sheets-Sheet 1 IIVV EV TOR. [flatly/Kenneth [slzler May 9, 1950 v [SHLER 2,506,874

- FILAMENT TENSIONING METHOD AND ELECTRICAL DEVICE HAVING IMPROVED FILAMENT TENSIONER 2 Sheets-Sheet 2 Filed June 8, 1946 46 I 9 INVENTOR. Harryll'armefih [.shler T-Ts -1 1 WWKM fir/ JMI,

' msflwbme Patented May 9, 1950 FILAMENT TEN SIONIN G METHOD AND ELEC- TRICAL DEVICE HAVING IMPROVED FILA- MENT TENSIONER Harry Kenneth Ishler, Floral Park, N. Y.', assignor to Sylvania Electric Products, Inc., a corporation of Massachusetts Application June 8, 1946, Serial No. 675,342

18 Claims. 1

This invention relates to electron tubes, more particularly to a novel structure and method for supporting and applying tension to a filamentary cathode in an electron tube.

In the manufacture of electron tubes having a filamentary cathode, it is usual practice for the cathode to be supported at one end by a bar, rod, or spring, which maintains the cathode under tension, and prevents it from vibrating or movmg during operation of the device. It is desirable that all electron tubes of a given construction shall have the same tension applied to the oathode so that the tubes will exhibit uniform electrical properties and be interchangeable in the various pieces of equipment in which they are designed to be used. Commonly the tension applied to the cathode of an electron tube of a given type depends upon the skill of the operator who is trained to hold the cathode in a desired tension and then weld or otherwise fasten the tensiomng member in position so that the proper tension is maintained. This practice is open to the diificulty that with variations in the skill of the different operators non-uniformity of work may result, and this also slows up production.

An object of the invention is to provide an improved method and structure for supporting and supplying tension to a filamentary cathode of an electron tube.

Another object of the invention is to provide an improved method and structure whereby a predetermined tension, particularly of low magnitucle, may be accurately applied to a cathode of an electron tube, especially of the miniature type.

Another object of the invention is to provide an improved filamentary cathode supporting structure whereby uniformity of tension of the filament is insured in the mass production of a given tube.

A still further object of the invention is to provide an improved method and structure whereby the tensioning of the cathode of an electron tube is determined principally by mechanical means rather than by the skill of the operator in assembling the device.

Further objects of the invention will manifest themselves as the description proceeds.

The practice of the invention permitting the foregoing and other objects to be attained will be described in connection with the accompanying drawings in which:

Fig. 1 is a sectional view along line l| of Fig. 2 of a complete electron tube employing one embodiment of the invention; V

Fig. 2 is a side elevation, partly in section, of the tube of Fig. 1;

Figs. 3 and 4 illustrate two stages in the process of assembling a filamentary cathode in the electron tube of Fig. 2;

Figs. 5 and 6 are enlarged views of the preformed cathode supporting member used in the tube of Fig. 2;

Fig. 7 is an isometric view illustrating more clearly the parts shown in Figs. 2 and 3, particularly the shape of the anchor member, and the threading of the filament through the mica supports;

Fig. 8 is a similar view to Fig. 7, showin the cathode assembly mounted in the anchor member;

Fig. 9 is an isometric view showing the welding of the cathode to the bottom support;

Figs. 10 and 11 are enlarged views of the preformed anchor member having sections in three planes; and

Fig. 12 is a side elevation of the tube of Fig. 2 but drawn to full scale.

In the accompanying drawing, for the purpose of illustration, the invention is embodied in a multi-electrode type of tube in which an envelope I encloses the electrode assembly including a filamentary cathode 2 and a cylindrical anode 3. Mounted within the anode and concentrically arranged are a control grid 4, a screen grid 5, and a suppressor grid 6. This electrode structure is supported between mica discs I and 8 which have apertures of suitable size and spacing to support the electrode assembly. The side rods of the grids and anode extend through these apertures and external connection is made with the elec-' trode elements by lead wires 9 which are sealed through a header l0 consolidated with the lower end of the envelope l. A lead wire I l is sealed through a tip formed in the top of the envelope I as shown particularly in Fig. 2.

The cathode and its component parts form a sub-assembly, and referring particularly to Figs. 2 and 3 it will be noted that a cathode 2 of the filamentary type has connecting tabs l2 and I 4 secured to the ends thereof. The tab I2 is adapted to engage a slot formed in a support l3 mounted on one of the lead wires 9 below the bottom mica 8. The L-shaped cathode tab I4 is attached to the opposite end of the filament 2 and is adapted to have secured thereto as by welding a tension spring l5. It will be noted that the tension spring I5 is bent intermediate its ends to form angular disposed portions of unequal length.-

Although it is not essential to give the spring a bend, the angle at which these portions are formed promotes uniformity of filament height.

It is obvious that the cathode structure described thus far may constitute a separate structure, assembled as a unit, which may subsequently be embodied in the main electrode structure during mounting of the cathode.

For supporting the top end of the cathode 2 there is provided an anchoring or bracket device, designated generally by reference character I6, said device being a preformed member having three plane sections I8, I9 and 20. Essentially the preformed connector member I6 comprises a body portion divided so as to form two side sections I9 and 20, said sections being derived by longitudinally bending said body portion substantially at right angles. The section I9 is transversely bent to provide a depending flap I8 which is slotted, by punching out a projection I! that forms a notch II into which notch the short end of the tension spring I is inserted and welded during the filament mounting operation. The anchor connecting member I6 is secured to the electrode assembly by welding side section 20 to a rigid rod, in this case the side rod of the suppressor grid 6. Care should be exercised during the welding of the section 26 so as not to distort the flap I8.

It will be noted that the flap I8 is initially angularly disposed with respect to section I9 and its slope in the illustrated arrangement (see Figs. 3 and 4) coincides with the unstressed initial slope of tension spring I5. The degree of the angle of the nap I 8 is a determining factor in the amount of tension eventually imparted to the tension spring I5. In the present illustration the angle y of the tension spring is about 110, and the inclination of the flap IS with respect to the side wall I9 is angle a: of about 20. Of course it will be understood that the size of the angles a; and 1 may be varied to suit the requirements of a particular cathode, which latter will vary in diameter, composition, and amount of tension desired on the cathode. The angles a: and 1 may also be varied to suit the dimension and composition of the tension spring I5. These variable factors are a matter of design, and therefore largely empirical.

By referring to the drawing, particularly Figs. 3, 4, 7, and 8, it will be seen that the depending flap portion I8 and side portion I9 of the connector member I6 form an apex at their junction, which apex functions as a relatively fixed fulcrum about which the spring I5 is tensioned by bending the flap I8 through angle a: so as to bring said fiap into engagement with the side portion I9 at the completion of the cathode mounting operation, presently to be set forth.

The method of mounting and tensioning the cathode will be understood from the following description. The cathode assembly as described above comprises a unitary structure consisting of the filament 2, tabs I2 and I4, and tension spring I5. The first step in the mounting operation is threading tab I2 through triangular apertures centrally located in the micas 'I and 8 (see Fig. 7). By having these apertures triangular shaped their areas may be restricted and yet permit the passage of tab I2; also the location of the apertures may be such that they are in axial alignment of the tube with respect to one of their vertices. The short end of the tension spring I5 is now inserted in the slot I'I provided in the flap I8. This positions the longer end of the spring I5 substantially parallel with the top mica I and 4 a uniform height therefrom, which features are obvious for reasons stated heretofore.

The operative next pulls tab I2 towards the header Ill until the tensioning portion of the spring I5 just moves, and while held in that position, tab I2 is welded in the slot in the bottom filament support I3. The final stage of mounting the cathode structure is applying tension to the filament 2 by closing the flap Ill, i. e. bending it through the angle a), previously or simultaneously welding side section !8 and tension spring I5 together.

From the foregoing description it will be seen, broadly the invention contemplates a tensioning means characterized by a spring element so mounted as to provide uniform tension even though the components which develop the tension are produced upon a mass production basis. This uniformity of tension is not only obtained by structural features but also by the method of spring mounting; for example, by having the tension spring at a uniform height from th top mica disc, and having all motion of the spring take place about a fixed fulcrum. This makes for precision with respect to the amount of tension and height developed by a given specification of parts and materials. Also my improved structure and method eliminates any welds on the resilient portion of the spring.

Another feature which is inherent in my construction is the provision of a spring anchorage having sufficient mass to provide effective cooling of the spring during the exhaust operation thus avoiding impairment of the tension in the spring that might otherwise be caused by heat encountered in the general fabrication processes employed in making electron tubes.

The bottom filament support I3 is so constructed as to act as a shield which contributes to the reduction of interelectrode capacitance in the tube, which structure is further described and claimed in my copending application Serial No. 683,302, filed July 13, 1946, and assigned to the present assignee.

It will be evident to those skilled in the art that modifications may be made as to the construction of the element comprising the cathode assembly as well as to the method of making the assembly. It is my intention to cover all of the aforesaid features as come within the scope of the appended claims.

I claim:

1. An electronic device including an electrical filament, and supporting means for said filament including a tensioning arm, a rigid support, and a connector, a portion of said connector being welded to said rigid support and another portion being secured to said arm and lying close and parallel to the adjacent part of said rigid support without however being directly secured to that support.

2. An electron tube having a filamentary cathode, and cathode-supporting means including a rigid support, a connector, and a resilient filament-tensioning arm secured to said connector, a first portion of said connector being welded to said rigid support, and a second portion of said connector being welded to said tensioning arm, said second portion lying as close as possible to said rigid support without however being directly secured thereto.

3. An electron tube having a filamentary cathode, and cathode-supporting means including a support doubled back on itself and a resilient filament tensioning arm secured to the doubled- 5. back portion of the support and arched across the end of the support.

4. An electron tube comprising a filament, and supporting means for said filament including a resilient tensioning arm and an apertured sheetmetal support, an end portion of said arm penetrating the apertured portion of said support and being welded thereto, and the adjacent portion of said arm lying against, but not being directly secured to, said sheet-metal support.

5. An electron tube including an hermetically sealed envelope containing an electrode assembly including a filamentary cathode, means securing one end of said cathode, and means including a formed member securing the other end of said cathode said formed member having a V-shaped portion having the legs of the V in contact with one another over substantially their entire length.

6. An electron tube comprising a main electrode assembly including a cathode sub-assembly comprising a filament having connecting tabs fastened to the ends thereof, one of said tabs being attached to a fixed support, the other tab being secured to a tensionspring bent intermediate its ends and forming angularly disposed portions of unequal length, the shorter of said portions being attached to a formed member suitably anchored and having an element angularly disposed with respect to its anchorage, the angularity of said element determining the amount of tension applied to said spring when the angular displacement of the element is changed during the mounting operation of the filament.

7. An electron tube comprising a main electrode assembly including a cathode sub-assembly, said cathode sub-assembly comprising a filament having connecting tabs fastened to the ends thereof, one of said tabs being attached to a fixed support, the other tab being secured to the end of a tension spring carried by a formed member, said formed member comprising a body portion divided into two side sections by bending said body portion longitudinally substantially at right angles, one of said sections being transversely bent to provide a depending flap receiving the unattached end of said tension spring, the apex formed by the junction of the flap and side portion constituting a fixed fulcrum for said tension spring when the flap is closed during the operation of mounting the cathode.

8. An electron tube comprising a main electrode assembly supported between top and bottom mica discs and including a cathode sub-assembly, said cathode sub-assembly comprising a filament having connecting tabs fastened to the ends thereof, one of said tabs being attached to a relatively fixed support, the other tab being secured to the end of a tension spring, said spring being bent intermediate its ends forming angularly disposed portions of unequal length, a formed member comprising a body portion divided into tygo side sections by bending said body portion longitudinally substantially at right angles, one of said side sections being transversely bent to provide a depending fiap receiving the end of the shorter portion of said tension spring, the other of said side sections being secured to a support wire, the angular displacement of the tension spring and the angular displacement of the flap being substantially of the same slope whereby when the respective parts thereof are united they coincide and the initial angular displacement of the fiap is the determining factor relative to the amount of tension ultimately to thetension spring; the apex of the flap and the body portion constitut ing a fixed fulcrum for tensioning the spring when the flap is closed during the operation of mount ing the cathode.

9. An electron tube comprising a main electrode assembly including a cathode sub-assembly, said cathode sub-assembly including afilament, an anchor member comprising two side sections bent at an angle with respect to each other, one of said side sections having a flap depending therefrom and angularly disposed with respect thereto, said flap being provided with a slot accommodating the end of a tension spring for supporting said filament.

10. An electron tube comprising a main electrode assembly including a cathode sub-assembly, said cathode sub-assembly including a filament, a preformed anchor member having sections in three planes, two of said sections constituting side elements one of which carries the third section as a depending flap angularly disposed with respect thereto, said flap being provided with a slot to accommodate one end of a tension spring, the other end of the tension spring being secured to an end of said filament, whereby the filament is placed under tension by the closing of said flap.

11. An electron tube comprising a main electrode assembly including a cathode sub-assembly, said cathode sub-assembly including a filament, a tension spring therefor, and apreformed anchor member, said anchor member comprising. sections occupying three planes, .two of .said sections constituting angled side elements, the third section constituting a depending fiap angul'arly disposed with respect to one of. said side sections, said flap. being provided with a slot to accommo date one end of said tension spring, the other end of the spring being secured to one end of said filament, the apex of the flap and the side section joined thereto constituting a fixed fulcrum for. tensioning said spring when the flap is closed during the operation of mounting the filament.

12. The cathode sub-assembly set forth in claim 9, wherein the tension spring is bent intermediate its ends forming angularly disposed portions of unequal length, the shorter portion of said spring being secured to the depending flap, the angularity of the flap and the shorter portion of the spring substantially coinciding, whereby when these parts are joined together the longer spring portion extends substantially parallel to and a predetermined height from the top mica of the main electrode assembly.

13. The cathode sub-assembly set forth in claim 6, wherein the angle of the spring portions is substantially degrees and the angle between the flap and its adjoining side section is substantially 20 degrees, the angularity of the longer section of said spring being the difference between the angles and determining the positioning of the longer spring portion with respect to the top mica disc.

14. An electron tube comprising a main electrode assembly comprising a structure supported between top and bottom mica discs and including a cathode sub-assembly, said cathode sub-assembly comprising a filament having tabs attached to the ends thereof, a connector rigidly securing one of said tabs below the bottom mica disc, a preformed anchor member supporting the tension spring substantially parallel to the top mica disc, said mica discs having apertures which align the filament concentrically and permit the passage therethrough of said tabs, and means imparting a predetermined tension to saidspring.

15. A support member for a tension spring in an electron tube including a bracket member having a pair of relatively movable arms, one of said arms being attached to a relatively fixed support rod, the other of said arms having means receiving a part of the tension spring so that upon relative movement of said arms a predetermined amount of proper tension will be placed on the spring.

16. The method of manufacturing electron tubes having a filament of predetermined length tensioned between fixed supports and having a resilient tensioning arm of predetermined resilience and having a bend of a predetermined angle intermediate its ends which comprises the steps of securing one end of said filament to a fixed support, securing the other end of said filament to an end of said tensioning arm, securing said tensioning arm to an angled support having a predetermined angle between the legs of said. angle whereby said filament is mounted under a nominal tension as controlled by said tensioning arm and then flattening said angled support to provide an accurately predetermined tension on said filament.

17. The method of imparting controlled tension to a filament of predetermined length comprising the steps of securing a V-shaped connector having a predetermined angle between the legs, of the V to a fixed support at one of its sides and to an end of a tensioning arm of predetermined resilience and having a bend of a predetermined angle intermediate its ends at the other of its sides with the tensioning arm extending across the apex of said V-shaped member, mounting the filament under nominal tension as determined by said tensioning arm, and pressing the portions of the V-shaped member against each other to increase the filament tension to a controlled degree.

18. The method of assembling a filament in an 8 electron discharge device wherein said filament is to lie substantially parallel to a fixed supporting rod and wherein said filament is to be tensioned by a resilient arm of predetermined resilience supported by said rod and having its active portion substantially perpendicular to said filament and said rod, said filament having a predetermined length, comprising the steps of securing a V-shaped interponent having a predetermined angle between the legs of the V to said rod with its apex pointing in the direction that the filament is to be urged for tensioning, bending said tensioning arm to provide an anchor part the slope of which is substantially the same as that of the unsecured arm of the V-shaped interponent when the other part of the arm lies substantially perpendicular to said rod, securing said anchor part of the tensioning arm to the unsecured portion of the interponent, mounting said filament under nominal tension as determined by said tensioning arm, and pressing the sides of said V- shaped member to lie against each other to impart controlled increased filament tension.

HARRY KENNETH ISHLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,522,286 Clausen Jan. 6, 1925 1,608,535 Schwerin Nov. 30, 1926 1,615,654 Ryder Jan. 25, 1927 1,774,698 Braselton Sept. 2, 1930 1,926,128 Van Steenis Sept. 12, 1933 2,100,306 McCarthy Nov. 23, 1937 2,303,278 IshJer Nov. 24, 1942 2,350,003 West May 30, 1944 FOREIGN PATENTS Number Country Date 243,785 Great Britain Nov. 30, 1925 

